Release of calcitonin gene-related peptide from the isolated mouse heart: methodological validation of a new model

Calcitonin gene-related peptide (CGRP), a potent vasodilator released from a subset of sensory Adelta- and C-fiber afferents, has been suggested to play a beneficial role in myocardial ischemia. Variations in CGRP release can possibly be correlated with diseases that involve changes in activity or degeneration of cardial afferent fibers. The aim of the present study was to evaluate a simple and easily reproducible model for measuring stimulated CGRP release from cardial afferents. For this reason freshly isolated mouse hearts were passed through incubations in series of 25 min. Solutions consisting of oxygenated synthetic interstitial fluid. Dissolved substances such as capsaicin, bradykinin and potassium chloride were used as excitatory test stimuli. For comparison, isolated mouse hearts were perfused with the same solutions through a cannula inserted into the rising aorta. The eluates were processed using an enzyme immuno-assay for measurement of CGRP concentrations. Capsaicin, bradykinin and the potassium solution caused concentration-dependent increases in CGRP release. There were no differences in CGRP release when oxygen was replaced by nitrogen in the solutions. Immersion of hearts caused significantly more CGRP release than perfusion with same solutions. The results suggest that mouse heart immersion is more effective than coronary perfusion in measuring stimulated CGRP release from cardial afferents which are widely distributed in the epicardium but rare in deeper myocardial layers. The results are discussed with respect to the potentially important vasodilatory and cardioprotective functions of CGRP released from activated epicardial afferents.